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Turning Sewage into Electricity in DC

Before embarking on our tour of the most advanced wastewater treatment plant in the country, our DC Water guide Yanique sets one thing straight.

“It’s not poop. It’s not crap. It’s nutrients.”

Using wastewater as a resource is a simple yet paradigm-shifting idea. At Washington DC’s Blue Plains facility, poop is a valuable commodity. Not only does this world-renowned facility filter wastewater from city sewers more thoroughly than any other plant in the nation, it’s now using human waste to generate electricity.

Most of us don’t think much about what happens to the stuff we flush down the toilet, or the stormwater that rushes into drains during a downpour. But the folks on the receiving end of those pipes know more about you than you’d probably care to think.

They know, for instance, what metro-DC residents are eating for dinner; what times of the day most people are visiting the loo (before they head home from work; halftime on Superbowl Sunday). They know when people leave town (the volume of sewage drastically decreases over winter holidays when many residents leave DC to visit family).

The evidence for all this is in Blue Plains’ influent screens. Yanique leads us into the headworks building where giant metal filters are catching all the trash that ends up in our sewer system. As you’d expect, it smells pretty rank in here. Conveyor belts run the length of the building carrying what looks like wet piles of lint, but upon closer inspection reveals itself to be candy wrappers, cigarette butts, tampon applicators, baby wipes, condoms, and yes, even rats.

All this unsightly detritus of humanity is pulled out of the water and trucked to a landfill. You can’t easily recycle stuff that’s been floating in sewage for hours, Yanique explains. A better approach is to keep it from getting here in the first place. DC Water was a strong advocate for the 5 cent bag tax instituted in DC and Montgomery County, Maryland in 2009 and 2012 and have subsequently seen a dramatic decrease in plastic bags in their screens.

From the headworks building, the unburdened water moves outside to an expansive series of sedimentation and reactor tanks where helpful bacteria work their magic. Unlike most water treatment plants in the US, Blue Plains also adds a nitrification and denitrification process that gets the water extra clean before it's discharged into the Potomac River. Dignitaries from all over the world come here to see what the future of water treatment looks like.

But that’s not the only reason Blue Plains is special.

At 25 megawatts, DC Water is the biggest user of electricity in Washington, DC. Inspired by Norwegian technology, the utility decided to address this by building the country’s first thermal hydrolysis system and anaerobic digester (the largest of its kind in the world). For the layman, that means turning poop into power.

By superheating the sludge that’s filtered out of Blue Plains’ tanks, and capturing methane to power turbines, the facility is generating over a third of its own electricity - or 10 megawatts - onsite. In ten years or so, Blue Plains plans to go net zero with the addition of solar panels. On top of all this, they’re also producing compost, similar to what you’d buy at the local home improvement store.

Unfortunately, because of runoff and sewer system capacity issues, lots of stormwater never makes it to Blue Plains for treatment. Instead, it runs along city streets picking up trash and pollutants and goes directly into the Potomac River. The city’s sewer system also overflows directly into the river during heavy rains. That’s why DC is spending billions of dollars to increase the sewer system capacity with new tunnels, and pushing green infrastructure projects like green roofs that filter rainwater where it falls.

Other challenges DC Water contends with? Climate change, for one. Blue Plains is located on riverfront vulnerable to flooding. As sea levels rise, Blue Plains, and the health of the Potomac, is in the crosshairs. The facility is also incapable of filtering microscopic manufactured pollutants like pharmaceuticals and endocrine-disrupting personal care products. These are yet more reasons to support strong laws against toxic chemicals and greenhouse gas emissions.

The operation that DC Water is running at Blue Plains shows how, with vision and ingenuity, we can take something that society considers a burden: wastewater, and turn it into something valuable: electricity and compost. Imagine what else we could accomplish with smart thinking like this in other industries?